Automated systems exist for collecting data from meters that measure usage of resources, such as gas, water and electricity. Some automated systems obtain data from such meters using a wireless network, that includes, for example, a central node in communication with a number of nodes (i.e., meters). Often, the wireless communications circuitry is incorporated into the meters themselves, such that each node in the wireless network comprises a meter having wireless communication circuitry that enables the meter to transmit its meter data. Electricity meters in such a network typically have wireless communication circuitry that permits the meter to both transmit and receive information to/from the central node. Such meters, or nodes, are referred to as bi-directional communication nodes. Bi-directional nodes are able to both transmit meter data to the central node and to receive data and instructions from the central node. In a network employing bi-directional nodes, nodes that are not within communication range of the central node may have their meter data relayed to the central node by one or more intermediate bi-directional nodes which serve as repeaters for the meter data of the transmitting node. Some networks operating in this manner are referred to as “mesh” networks.
Some meters, however, such as many water and gas meters, are only capable of transmitting meter data; they are not capable of receiving information or instructions from a wireless node. Such “one-way” nodes must always depend on the bi-directional nodes in the network to relay their meter data to the central node. An exemplary wireless network employing such nodes is depicted in FIG. 1.
As shown, central node 116 collects and stores data from a number of meters (i.e., nodes). Bi-directional nodes 221-231 may include bi-directional transmitting and receiving devices with a wireless communication path to the central node 116 that is either a direct path or an indirect path through one or more intermediate bi-directional nodes serving as relay nodes. For example, bi-directional nodes 221 and 222 have direct communications paths to central node 116, while bi-directional nodes 223-231 have indirect communications paths to central node 116 through one or more intermediate nodes. In some networks (such as the exemplary network shown in FIG. 1), each bi-directional node 221-231 has a single, designated path to the central node 116, while, in other networks, multiple dynamic paths may exist between each bi-directional node and the central node. In networks where each bi-directional node 221-231 has only a single, designated path to the central node 116, only those nodes along the designated path will relay a message from the node with that designated path. In other networks, multiple bi-directional nodes may relay, or retransmit, a message from a given node.
So-called “one-way” or “transmit-only” nodes 251-256 may include transmit-only meters such as water or gas meters. The transmit-only nodes 251-256 may gather and transmit meter data that is then relayed by one or more bi-directional nodes 221-231 to the central node 116. The system depends on the transmissions from a transmit-only device being received by at least one bi-directional node and then relayed through the network to the central node 116. Each bi-directional node may be within range and capable of receiving meter data directly from multiple transmit-only nodes. For example, bi-directional node 228 is capable of receiving meter data directly from transmit-only nodes 252-254. Consequently, the meter data transmitted by a given transmit-only node may be received by multiple bi-directional nodes and thus relayed through the network to the central node multiple times.
An advantage of the above described system is that it provides redundancy with respect to the transmission of meter data from the transmit-only meters to the central node. Specifically, because each transmit-only node may be in direct communication range of several different bi-directional nodes, multiple different communications paths may exist from each transmit-only node to the collector. For example, transmit-only node 253 may transmit its meter data to the central node 116 via a first communications path (253>227>223>221>116), a second communications path (253>228>224>222>116), or a third communications path (253>229>225>222>116). These multiple communications paths are advantageous because, even if one or more of the bi-directional nodes are not functioning properly, there is still a high probability that the meter data will be successfully relayed from the transmit-only node to the central node. For example, even if node 227 is not functioning properly, thereby rendering unsuccessful the first communications path described above, transmit-only node 253 can still successfully transmit its meter data to the central node 116 via the second or third communications paths.
While redundancy can help to provide successful data transmission, too much redundancy can be problematic because it results in too many bi-directional nodes transmitting the same meter data back to the central node. This places an unnecessary burden on the system from an overall communications traffic point of view, and this problem is exacerbated when meters are located several hop distances away from the central node. In some networks, the bi-directional meters are only allocated a fixed time period (e.g., an “exception” time) in which to relay all of their meter data to the central node. When a bi-directional meter has received meter data from a large number of transmit-only nodes, it is possible that the bi-directional meter will need to relay more data than it is able to transmit within the fixed time period. If the bi-directional meters cannot relay all of their meter data within the fixed time period, then separate individual “polled” requests may need to be issued by the central node to retrieve the excess meter data.
Thus, there is a need for a more efficient mechanism for meter data from transmit-only nodes to be received and propagated through the network to the central node.